This application is a response to the NIH-NIAID RFA for Expansion of the Pediatric AIDS Clinical Trials Group (ACT) via funding of cooperative agreements with several pediatric centers. We propose to develop a single, collaborative pediatric ACT center at the Johns Hopkins University School of Medicine and the University of Maryland, the two institutions that follow the great majority of children exposed to human immunodeficiency virus (HIV) infection within the City of Baltimore. The combined institutions have experience with approximately 132 children with HIV infection or children born to HIV infected mothers. Active programs exist at each institution for primary care of children exposed to HIV infection and each program is committed to clinical investigation of several aspects of pediatric HIV infection. In addition, Phase II trials of zidovudine use in children with symptomatic HIV infection are just underway at Johns Hopkins, and a Phase I protocol to study the pharmacokinetics and safety of zidovudine in newborn infants will begin soon. This collaboration brings together clinical investigators with expertise in pediatric infectious diseases, pediatric immunology, primary care pediatrics, obstetrics, laboratory diagnosis of HIV infections, and clinical pharmacology. Some of these investigators also have considerable experience in study design, project coordination, data management, and biostatistics. Additional staff will include pediatric practitioners, social workers, and laboratory personnel. The Baltimore Pediatric ACT expects to participate in those protocols generated by the Collaborative Pediatric ACT in which we can make a contribution to the overall effort and which are compatible with our own treatment and research objectives. This includes the study of specific antiviral agents, immunomodulating therapy, and drugs for management of the opportunistic infections associated with pediatric AIDS. We also expect to assume a leadership role without the AIDS Clinical Trials Group in certain areas, particularly the study of antiviral agents and other therapeutic modalities that might modify or prevent HIV infection in newborn infants. This objective complements our ongoing research into the mechanism and risk factors for vertical transmission of HIV.